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1953-54 Theatre Catalog, 11th Edition, Page 16 (xvi)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 16
Page 16

1953-54 Theatre Catalog, 11th Edition, Page 16

volume or cubical content of the auditorium structure in its relationship to the seating capacity.

From their research and personal studies Potwin and Schlanger found that when the length of a theatre auditorium became greater than twice the width, difficulties arOSe from a multiplicity of sound reflections occuring between the side wall surfaces. When the ratio of width to length was less than 1 to 1.4, the resulting design became unfavorable from the standpoints of proper sound distribution and vision. Furthermore this design created an unusually large rear wall, which was often a source of objectionable sound reflections.

Establishing the ceiling height in its most practicable and best acoustical relationship to the horizontal dimesnions, was the next element that these two men studied. They considered ceiling height very important because it affected both the proportions and the structural volume of the auditorium.

From an architectural viewpoint, the determination of ceiling height is governed by three factors. They are sightline requirements; width of the light beam and its projection angle to the

screen; and the general appearance of the auditorium. From the acoustical standpoint, Schlanger felt that two other important factors should be included in the determination of ceiling height. These were the proper relationship of the ceiling height dimensions to the horizontal proportions; and the optimum cubic-foot volume per seat required for a given design.

One of the things which Schlanger and Potwin found to be wrong, from an acoustical point of view, was the excessive ceiling heights that were found in many theatre auditoriums. The large structural volume per seat and the prolonged rcverberation time resulting from this acoustical defect in theatre planning produced a need for corrective materials in many new theatres.

Using a 900 seat house as their model they decided that the structural volume of an auditorium seating that many persons, should lie between 120 and 130 cubic feet per seat. The factors affecting the determination of these limits are the optimum or best times of reverberation at different frequencies for reproduced


sound, and the fixed and variable soundabsorption required to produce these times of reverberation.

Fixed absorption refered to the absorption provided by theatre chairs, carpets, and interior surfaces of standard furred construction, finished in an ordinary manner. Variable absorption is the absorption normally provided by the audience, Optimum reverberation times are usually based on an audience condition approximating two-thirds of the house seating capacity.

The chairs constitute the major part of the fixed absorption for a theatre initially planned to be acoustically functional in design. To ensure a major change in the reverberation time, Schlanger agreed that it was very important that these chairs be of an efficient upholstered type. A 20-inch chair was found to have a sound absorption value equivalent to more than two-thirds that of the average person.

From the standpoint of vision, Schlanger said that the proportions and cubicfoot volumes of auditoriums varied for a number of reasons. One was the type of seating arrangement used in the horizontal dimension of the auditorium,

determined by the number of seats and aisles to be arranged across the width of the auditorium. Another was the type of seating arrangement employed in the vertical dimension of the auditorium. Still another important factor was the inclination or inclinations of the floor for the main or orchestra level.

The degree of inclination of the floor in all cases is affected by the manner in which the seats are placed behind each other. When these seats are arranged in staggered fashion so that the center of any seat is always directly behind the dividing armblock of the preceding seat, Schlanger and Potwin said that thc'inclination of the Hoor may be reduced by almost one-half. They felt that variations in the floor inclination was important in the question of acoustics because they directly affected the hcight and inclination of the upper level seats and the placing of the pros jection room, thereby the total height of the auditorium.

After a great deal of study Schlanger and his co-workcr concluded that there were a number of advantages to be

gained by constructing theatres with lower ceiling heights. These were a lOWer initial time of reverberation, resulting from a smaller volume per seat; reduces surface areas to be treated acoustically, permitting more efficient control of sound by shaping the interior surfaces; and the economies realized in construction costs through the elimination, or reduction in quantity, of acousu tic materials usually required, as well as through the use of smaller quantities of ordinary building materials.

Some other advantages which they found to result from the proper control of ceiling height and structural volume, were that economies in the size and capacity of sound-reproducing systems were frequently made possible in theatre auditoriums having reduced volumes per seat. Another was that excessive power output was not required to compensate for high energy losses frequently caused by the use of acoustic materials on wall or ceiling surfaces.

The final phase of theatre planning which Schlanger and Potwin decided influenced both the acoustical condition and the architectural treatment was the detailed shaping or styling of the surfaces within the auditorium. This phase of planning was said to be very important because it dealt with the proper determination of basic outline and structural volume to control the character of sound and the destination of sound redections.

When an auditorium was to be used for direct speech or music presentations, it was desirable to plan and arrange the interior surfaces so as to aid in reinforcing the sound produced on the stage. They contended however, that in the motion picture theatre, where sound was reproduced and adequate power could be produced electrically, the acoustical problem was not one of designing surfaces to gain reinforcement. Rather the interior surfaces of this auditorium


' neutral auditorium treatment is seen here in the

Bell. Walls were shaped in acoustic form.

should be shaped and arranged so that. they function to break up or disperse sound energy. In their opinion this result . could be accomplished most Successfully in cases where favorable basic propore tions were maintained, and where theinitial time of reverberation was efficie ently controlled by the structural volume of the auditorium.

Schlanger said that irregularity of surfaces arranged to break up or disperse sound energy could take. the form of angular or sloping sections, now symmetrical broken offsets, or convex projections. The size of each surface unit, its position and arrangement on a wall 01' ceiling, and its degree of projection from a horizontal or vertical line would depend upon the requirements for control of the destination and dispersion of sound reflections in the individual design. The surface of a major angular or convex projection may in turn be broken into smaller increments if rew quired in special cases for dispersion of the very high frequencies.

One of the major conclusions that Schlanger and Potwin drew from their

1953-54 Theatre Catalog, 11th Edition, Page 16